The invention generally relates to a gas turbine blade. More preferably, it relates to one with an inner cavity for the guidance of a cooling fluid.
Such a coolable gas turbine blade is shown in U.S. Pat. No. 5,431,537. Gas turbine blades are exposed to extremely high temperatures by the hot gas flowing around them. They therefore have to be cooled. The inlet edge of a gas turbine blade is exposed to particularly high thermal loads. For this reason, the inlet edge must be cooled particularly intensively.
In the case of cooling using cooling air, the aim is to achieve as low a consumption of cooling air as possible, since the cooling-air consumption lowers the efficiency of the gas turbine. To improve the cooling, turbulators are provided on the inside of the gas turbine blade, which swirl the cooling medium and thus permit better heat transmission. In the gas turbine blade of U.S. Pat. No. 5,431,537, the turbulator configuration both achieves a beneficial cooling of the inlet edge and affords advantages regarding the castability of the turbine blade.
U.S. Pat. No. 5,320,483 shows a steam-cooled gas turbine blade. Steam cooling is more favorable in terms of the efficiency of the gas turbine. It requires a closed cooling circuit, however, since, in contrast to air, steam cannot be introduced from the blade into the hot-gas duct. For cooling the inlet edge, an impact-cooling insert is used, which guides steam into a duct according to the contour of the inlet edge, steam being conducted from this duct, via bores, against the inlet edge with an impact-cooling effect. This design is highly complicated in manufacturing terms and, furthermore, also leads to an inlet edge which is comparatively thick and therefore not optimized aerodynamically.
An object of the invention is to specify a gas turbine blade, in which it is possible for the inlet edge to be cooled in a simple way in terms of production and at the same time in an aerodynamically favorable way.
According to the invention, this object is achieved by, for example, specifying a gas turbine blade directed along a blade axis, with a profile including a suction side, a delivery side, an inlet edge and a flow-off (outlet) edge. An inner cavity is preferably included in the profile for the guidance of a cooling fluid, with the cavity including an inlet edge cavity adjacent to the inlet edge and a first part cavity adjoining the inlet edge cavity in the direction of the flow-off edge. The first part cavity is preferably divided into a first subspace and a second subspace by a partition extending in a direction from the inlet edge to the flow-off edge. Cooling fluid is capable of being introduced from the first subspace via impact-cooling orifices into the inlet edge cavity and from there into the second subspace with an impact-cooling effect on the inlet edge.
By way of this configuration, for the first time, the course is adopted of preceding the inlet edge region by a divided cavity, so that a closed cooling fluid guidance becomes possible in a structurally simple way. This construction avoids an impact-cooling insert of complex design in the region of the inlet edge and, furthermore, makes it possible to design the inlet edge in the most aerodynamically favorable way.
Preferably, the inlet edge cavity is separated from the first part cavity by a half-rib connected to the profile. Such a half-rib does not extend from the suction side as far as the delivery side, as is otherwise customary in gas turbine blades, but, instead, terminates in the cavity. For example, where a cast gas turbine blade is concerned, such a half-rib may be cocast. Cooling fluid is then guided from the first subspace via the half-rib into the inlet edge cavity, impact-cooling orifices being provided for this purpose in the half-rib. These impact-cooling orifices are also preferably designed as slots. Such a slotted half-rib can be produced simply in manufacturing terms and at the same time affords optimum impact-cooling conditions.
Preferentially, the first part cavity includes, adjoining it in the direction of the flow-off edge, a second part cavity which is separated from the first part cavity by a rib extending from the suction side to the delivery side. The cooling fluid is capable of being introduced through ducts in the rib from the second subspace into the second part cavity. Also preferably, in this case, the cooling fluid is capable of being guided in the first subspace parallel to the blade axis, in the second subspace transversely to the blade axis and in the second part cavity parallel to the blade axis. This results in the configuration where the cooling fluid in the two subspaces of the first part cavity has two flow directions directed perpendicularly to one another.
The partition is preferably a metal sheet. This affords a further simplification in manufacturing terms, precisely where cast gas turbine blades are concerned, since a partition does not have to be cocast. The partition is simply inserted into the ready-cast blade. Preferentially, in this case, the partition is clamped in clearances between cast-on turbulators and/or is added to an offset which, in particular, is cast on a rib. The partition also preferably separates the second subspace from the inlet edge cavity, the partition having orifices for introducing the cooling fluid from the inlet edge cavity into the second subspace. This design is particularly preferred in conjunction with the half-rib separating the inlet edge cavity from the first subspace. Thus, by using the half-rib on the one hand, and the partition inserted as a metal sheet on the other hand, the inlet edge cavity is separated from the first part cavity. In this case, the metal sheet is preferably supported on the first half-rib.
The gas turbine blade is preferably designed as a guide blade.
The cooling fluid is preferentially steam.
Steam cooling affords the advantage of a saving of cooling air and thus leads to an improvement in efficiency and in increase in power for the gas turbine. A steam supply can be used effectively precisely where guide blades are concerned, since the guide blades are connected to the casing, via which the cooling steam can be supplied.